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Mystery bacteria 'cobwebs' found in SRS cooling tank

By MIKE GELLATLY

May 4 2013 11:31 pm May 4 11:35 pm

Spring cleaning is always a good way to get rid of those hard-to-reach cobwebs that appear around the house. However, when they appear in cooling tanks for spent nuclear fuel and have never been seen there before, special attention is warranted.

Sometime in Fiscal Year 2011, “cobwebs” of bacteria were first discovered in the L Area basin at the Savannah River Site. Since then, a process of getting to the 70-feet-deep life form, collecting it and then examining it has been undertaken.

The formations of bacteria are colloquially described as “cobwebs” as they form strands similar to the household dust collections.

In an April 23 presentation to the SRS's Citizen Advisory Board's Nuclear Materials subcommittee, Maxcine Maxted with Department of Energy noted advances that had been made in approaching, recovering and analyzing the bacterial growth located on the tops of the fuel bundles underwater.

“The cobweb material was collected by pumping it through bag filters on a cart located on zero level in the basin,” explained Amy Caver of DOE Public Affairs.

Maxted said that the bacteria would be killed before being studied. In previous, somewhat similar cases, such bacteria has been killed with hydrogen peroxide.

“Without the external nutrients, the bacteria cannot sustain themselves. Infrared from the measured levels of microbial diversity measured these requirements are currently being met. Sampling for organic carbon in multiple basin locations was unable to determine a definitive source of external carbon for the bacteria,” Caver said.

Not knowing the “food” source for these bacteria adds to the mystery.

For a corrosion precaution and to improve fuel bundle identification, the cobwebs will be removed from the fuel bundles by underwater vacuuming.

But, however the strands formed, they are posing no danger to the storage facilities.

“The cobweb material density has not noticeably increased since the original mapping in December 2011,” Caver said. “In the locations where the cobweb material was removed during sampling in January 2012, there has been little to no cobweb material reformation. Cobweb material has not spread to other sections of the basin. There has been no noticeable corrosion of the aluminum materials in the areas with the cobweb material.”

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